This invention related to a printer which prints information on a continuous form by transferring toner images thereonto, and more particularly to a justification system for controlling the printing so as to accord with the rules on the continuous form.
Conventionally, there is known an image recording device that utilizes a so-called electrophotographic system, in which a surface of a photoconductive drum is exposed to light to form a latent image on the drum surface, toner is applied to the latent image to develop the image, and the developed image is transferred onto a recording sheet material and fixed by a fixing unit. Such image recording devices are chiefly employed in copying machines. In recent years, however, the image recording device is being utilized in a printer and the like for printing the output from a computer.
In a copying machine, in general, cut sheets are used as the recording sheet material, and a heat-roll fixing system is utilized, wherein the toner is fixed by a combination of heat and pressure. In addition, a presure fixing system has recently been developed, which is low in electric power consumption and which does not require a long amount of time for preheating the heat rolls.
However, in a printer it is desired to use a continuous recording form as the recording material, the recording material form being identical with that used in a conventional line-printer. The continuous recording form is a folded continuous recording form (hereinafter referred to simply as "continuous form") called a fan folded form which has sprocket holes formed therein along its edges. Perforation marks are provided at each of the folded sections to enable sheet sections to be easily severed from each other. Horizontal rules are marked at predetermined intervals in a longitudinal direction between the perforations with a predetermined positional relationship with respect to the sprocket holes.
In the above printer, a continuous form having carried thereon unfixed toner image is clamped and passed between a pair of rotating fixing rolls so that the toner image is fixed onto the continuous form.
Usually, the continuous form is driven to travel by rotation of the fixing rolls. The continuous form is transported at a speed that is adjusted to accord with a predetermined relationship between a print segment on the continuous form and a number of main scannings on the photoconductive drum.
In the meantime, the printer employing the fan-folded form defines a non-printing area around the perforation because the form is cut into separate sheets at the perforations after printing.
In the printer described above, however, expansion or contraction of the continuous form, due to humidity, variations in the diameter of the fixing rolls, changes in the thickness of the continuous form at the fixing rolls and so on, cause variation in the time to feed each print segment (equal time required for passing of the leading and tailing ends of the print segment at a certain point in the travel path of the continuous form). This variation influences the predetermined relationship between the print segment and the main scanning number, thus shifting the printing position relative to the rules.
Further, the motors that are utilized for scanning the photoconductive drum and the exposure system vary in their rmp (revolutions per minuite) due to variations in the supply voltage and ageing. Thus, even if each printing segment of the continuous form is fed at a constant rate, the associated area of the photoconductive drum is shifted out of position and the printing position slips away from the rules, resulting in an undesired impression.
Moreover, the continuation of the printing accumulates such errors, making the rules meaningless. In the worst case situation, printing occurs at the nonprinting areas around the perforations.